gms | German Medical Science

Objective: Cervical spine computed tomography (csCT) is the modality of choice for pre-surgical evaluation of osseous foraminal stenosis and central spinal stenosis as a result of ossification of the posterior longitudinal ligament (OPPL) or stenotic osteophytes. However, radiation dose of csCT is crucial especially in younger patients due to a non-negligible irradiation of the thyroid gland. With the introduction of 3rd generation dual source CT (DSCT) 150 kVp imaging with spectral beam shaping by means of a dedicated 0.6 mm Sn filter has become clinically available. High tube voltage settings are generally superior to standard CT protocols for the assessment of high contrast structures but were traditionally associated with a higher radiation dose when compared to standard 120 kVp protocols. The novel 150 kVp protocol with additional Sn filtration generates a sharper x-ray beam spectrum which filters low energy photons of the polyenergetic x-ray beam. The aim of this prospective study was to evaluate this novel csCT protocol in patients with suspected osseous stenosis in comparison to a standard csCT protocol.

Methods: 59 patients with suspected cervical foraminal stenosis prospectively underwent csDT using a 150 Sn protocol as well as a standard 120kV protocol on a 3^rd generation dual-source CT. Radiation dose parameters (DLP and CTDIvol) were recorded and compared between both protocols. Furthermore, image quality was subjectively and independently evaluated by an experienced neurosurgeon and radiologist in direct comparison using a 5 point Likert scale regarding overall image quality, foraminal stenosis and other relevant pathologies.

Results: The DLP (dose-length product) and CTDI (CT dose index) were significantly reduced using the new protocol. In 59 proceeded images we found a mean radiation dose reduction of 34,4% (DLP) and 37,5% (CTDI). The image quality overall was rated superior by the radiologist in 54 of the 59 cases and in 52 by the neurosurgeon. Foraminal stenosis analysis showed the highest subjective image quality score 5 [range 4-5] in the new protocol. The standard 120 kVp datasets image quality was rated inferior in comparison to the new protocol (120 kV: 4 [range 3-5]. Evaluation of disc herniations was also rated superior using the 150 kV protocol (mean score 4 vs 3).

Conclusion: csCT performed with 150 kV Sn filtration leads to a significant radiation dose reduction when compared with standard 120 Kv csCT. Furthermore, the image quality of the novel 150 Sn csCT protocol has shown to be superior to previous standard protocols. This new image modality could therefore aid to improve individual surgical strategies due to the superior image quality whilst simultaneously reducing the preoperative radiation exposure of patients. Additional studies are needed to determine whether soft tissue pathologies, in particular herniated discs, can be sufficiently ascertained.